Lý thuyết axit bazo

Khái niệm axit, baz a Thuyết cổ điển Arrhenius b Thuyết proton Bronsted c Thuyết electron Lewis Thuyết cổ điển Arrhenius Axit: chất điện ly cho ion H3O+ nước HCl(aq) +H2O(l) H3O+(aq) + Cl-(aq) HNO3(aq)+H2O(l) H3O+(aq) + NO3-(aq) Baz: chất điện ly cho ion OH- nước NH3(aq) + H2O (l) NH4+(aq) + OH-(aq) Thuyết proton Bronsted Axit :cho proton HA  H+ + ABaz: nhận proton: B + H+  BH+ Các cặp axit – baz liên hợp: HA/A- , BH+ /B HA + B  A- + BH+ Phản ứng axit baz pư trao đổi proton(H+) axit 1cặp axit- baz liên hợp với 1baz cặp axit-baz liên hợp khác Phản ứng cặp axit baz liên hợp Cặp liên hợp Acid + Base Base + Acid Cặp liên hợp Reaction HF + H2O F– Reaction HCOOH + CN– HCOO– Reaction NH4+ + CO32– NH3 Reaction H2PO4– + OH– HPO42– + H2 O Reaction H2SO4 + N2H5+ HSO4– + N2H62+ Reaction HPO42– + SO32– PO43– + + H3 O+ HCN HCO3– + + HSO3– Dự đoán axit, baz Bronsted Axit – chất phải chứa H+ Phân tử trung hồ : HCl, HNO3, HF… Cation có chứa H+ : NH4+ Anion có chứa H : HSO4- , H2PO4- … Cation kim loại nước : Fe2+(aq) ; Al3+(aq) Cation cấu hình khí trơ có q2/ r lớn → tính axit mạnh Cation có điện tích bán kính tương đương, cấu hình: 18e – (18e +2e) – (18e> >8e ) → tính axit mạnh cấu hình 8e 3+ Al(H2O)6 Al(H2O)63++H2O (l) Al3+(aq) bị thuỷ phân 2+ Al(OH)(H2O)5 + H+ 2+ Al(OH)(H2O)5 + H3O+ Baz Bronsted - chất có dư mật độ điện tích âm Anion: Cl-, NO3-, SO42-, PO43-… Phân tử cộng hoá trị phân cực : NH3 Chất lưỡng tính- chất vừa có khả cho H+ vừa có khả nhận H+ Các hợp chất có chứa H thường chất lưỡng tính HCl + H2PO4-  Cl- + H3PO4 H2PO4- + HCO3-  HPO42- + H2CO3 pK a (H 3PO ) = 7,21 pK a (H CO ) = 10,33 CƯỜNG ĐỘ AXÍT BAZ Ở TRẠNG THÁI KHÍ B(k) + H+(k) → BH+(k) ∆H = -AP AP – lực proton baz B AP dương →B baz mạnh →BH+ axit yếu AP phụ thuộc vào mật độ electron trung tâm tiếp nhận H+ ẢNH HƯỞNG CỦA BÁN KÍNH ANION ĐẾN AP ANION F- Cl- Br- I- AP(kJ/mol) 1554 1398 1354 1315 Bán kính anion tăng dần →mật độ electron anion giảm dần →AP giảm dần →tính baz giảm ẢNH HƯỞNG CỦA LIÊN KẾT ĐẾN AP Phân tử NH3 PH3 AsH3 AP(kJ/mol) 850 789 Khả lai hóa giảm dần → mật độ electron giảm → AP giảm Acid-Base Reactions in Aqueous Solutions • The total ionic equation is: You it! CH3COOH(aq) + NH3(aq) → NH4+(aq) + CH3COO-(aq) • The net ionic equation is: You it! CH3COOH(aq) + NH3(aq) → NH4+(aq) + CH3COO-(aq) Acidic Salts and Basic Salts • Acidic salts are formed by the reaction of polyprotic acids with less than the stoichiometric amount of base • For example, if sulfuric acid and sodium hydroxide are reacted in a 1:1 ratio H2SO4(aq) + NaOH(aq) → NaHSO4(aq) + H2O() The acidic salt sodium hydrogen sulfate is formed • If sulfuric acid and sodium hydroxide are reacted in a 1:2 ratio H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O() The normal salt sodium sulfate is formed Acidic Salts and Basic Salts • Similarly, basic salts are formed by the reaction of polyhydroxy bases with less than the stoichiometric amount of acid • If barium hydroxide and hydrochloric acid are reacted in a 1:1 ratio You it! Ba(OH)2(aq) + HCl(aq) → Ba(OH)Cl(aq) + H2O() The basic salt is formed • If the reaction is in a 1:2 ratio Ba(OH)2(aq) + 2HCl(aq) → BaCl2(aq) + 2H2O() The normal salt is formed Acidic Salts and Basic Salts • Both acidic and basic salts can neutralize acids and bases – However the resulting solutions are either acidic or basic because they form conjugate acids or bases • Another example of BrØnsted-Lowry theory • This is an important concept in understanding buffers • An acidic salt neutralization example is: NaHSO4(aq) + NaOH(aq) → Na2SO4 (aq) + H2O() • A basic salt neutralization example is: Ba(OH)Cl(aq) + HCl(aq) → BaCl2(aq) + H2O() The Lewis Theory • Developed in 1923 by G.N Lewis – This is the most general of the present day acid-base theories – Emphasis on what the electrons are doing as opposed to what the protons are doing • Acids are defined as electron pair acceptors • Bases are defined as electron pair donors • Neutralization reactions are accompanied by coordinate covalent bond formation The Lewis Theory • One Lewis acid-base example is the ionization of ammonia + → NH + H 2O ← NH + OH base acid The Lewis Theory • Look at this reaction in more detail paying attention to the electrons + H H NN HH HH ++ H H O O N H H H + H H HH Base - it donates the electron pair H H H Acid - it accepts the electron pair Notice that a coordinate covalent bond is formed on the ammonium ion O - The Lewis Theory • A second example is the ionization of HBr HBr + H2O → H3O+ + Br- acid base The Lewis Theory • Again, a more detailed examination keeping our focus on the electrons H H Br Br H H + Acid - it accepts the electron pair + O O Br Br H H Base- it donates the electron pair + + + + H H O O H H H H covalent coordinate bond formed The Lewis Theory • A third Lewis example is the autoionization of water You it + → H O + H O ← H 3O + OH acid base The Lewis Theory • The reaction of sodium fluoride and boron trifluoride provides an example of a reaction that is only a Lewis acid-base reaction – It does not involve H+ at all, thus it cannot be an Arrhenius nor a Brønsted-Lowry acid-base reaction NaF + BF3 → Na+ + BF4• You must draw the detailed picture of this reaction to determine which is the acid and which is the base The Lewis Theory FF ++ FF Base - it donates the electron pair FF F BB B FF Acid - it accepts the electron pair FF F F F coordinate covalent bond formed The Lewis Theory • BF3 is a strong Lewis acid Another example of it reacting with NH3 is shown in this movie The Lewis Theory • • Look at the reaction of ammonia and hydrobromic acid NH3 + HBr → NH4++ BrIs this reaction an example of: • Arrhenius acid-base reaction, Brønsted-Lowry acid base reaction, Lewis acid-base reaction, or a combination of these? You it! It is a Lewis and Brønsted-Lowry acid base reaction but not Arrhenius The Preparation of Acids • The binary acids are prepared by reacting the nonmetallic element with H2 H2(g) + Cl2(g) → 2HCl(g) This reaction is performed in the presence of UV light • Volatile acids, ones with low boiling points, are prepared by reacting salts with a nonvolatile acid like sulfuric or phosphoric NaCl(s) + H2SO4(conc.) → NaHSO4(s) + HCl(g) NaF(s) + H2SO4(conc.) → NaHSO4(s) + HF(g) ... dung môi axit acetic Cường độ axit HnX dd nước Cường độ oxiaxit HaXOn(OH)m • n=0 axit yếu • n=1 axit yếu • n=2 axit mạnh • n=3 axit mạnh Pauling pK1 = 7-5n ; pK2= pk1+5 ; pK3= pk2+5 …… Các axit có... H2D+ Kd = [D-][H2D+] Sự điện ly axit baz kết pư trao đổi proton axit baz với dung môi NH3(aq) + H2O (l) baz axit NH4+(aq) + OH-(aq) axit baz Sự điện ly axit baz nước Axit: HA + H2O  A- + H3O+ [... OH-(aq) Thuyết proton Bronsted Axit :cho proton HA  H+ + ABaz: nhận proton: B + H+  BH+ Các cặp axit – baz liên hợp: HA/A- , BH+ /B HA + B  A- + BH+ Phản ứng axit baz pư trao đổi proton(H+) axit